Telephone ringer



Jan. 6, 1942 J. D. HUBBELL ET AL 2,269,108

TELEPHONE RINGER Filed March 14, 1939 J. D. HUBBELL C .f. W/EBUSCH INVEN TORS A 7' TORNE V Patented Jan. 6, 1942 UNITED STATES PATENT OFFICE TELEPHONE RINGER James D. Hubbell, East Orange, N. J and Charles F. Wiebusch, New York, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 14, 1939, Serial No. 261,698

6 Claims.

This invention relates to electromagnetically operated devices and particularly to polarized ringers of the type extensively used for signaling purposes in telephone systems.

It is the object of this invention to provide an improved type of biased telephone ringer which is particularly suitable for operation on rectified current pulses of relatively low magnitude.

This object is attained in accordance with a feature of the invention by the provision of means, in a polarizedringer structure, which functions to oppose the movement of the ringer armature, when the ringer is energized, with a force which is equal to and opposite in effect to that produced by the permanent magnetic airgap flux. More specifically, the ringer armature .has permanently afiixed thereto a sheet spring whose free end engages the ringer electromagnet core asthe armature is actuated and is flexed as the armature end approaches the core end to exert'an opposing influence upon the armature. The magnitude of the opposing influence upon the armature is determined by the natural stiffness of the spring imparted to it by its physical characteristics and dimensions, which are such as to cause the spring to counterbalance the force exerted upon the armature by the permanent magnetic air-gap flux. The balancing spring, therefore, acts to maintain the armature in a condition of balanced equilibrium-in so far as the influence of the permanent magnetic air-gap flux upon the armature is concerned, thereby substantially obviating the necessity for applying an appreciable initial bias to the armature to insure its return tonormal position after the ringer ens 'erg izing current has been removed or interruptrelated feature of the invention permits the usual armature-biasing spring to serve merely in the'capacity of Vernier to the balancing spring thereby maintaining a relative ease of adjustmanner in which a ringer designed in accord- 55 ance with the present invention may be associated with a telephone subscribers line circuit for operation by rectified current pulses; and

Fig. 5 is a schematic illustration of the mag- 'neti-c circuit embodied in the ringer design.

The ringer structure shown in Fig. 1 includes a U-shaped permanent magnet l which is magnetized so as to have a consequent pole at its "center and whose upper ends are bridged by a gong-supporting bracket of magnetic material comprising the bridge portion 2 and the gongsupporting portion 3, the plane of the latter being substantially at right angles to the plane of the former. The bridge portion 2 is secured to the ends of the permanent magnet 1 preferably by welding the parts together. The gong-supporting portion 3 terminates in two diverging earlike projections 4 and 5, to the ends of which the gongs 6 and I are secured by means of screws 8 and 9, respectively. The gongs are eccentrically mounted to permit adjustment thereof relative to the striker l0.

The ringer electromagnet consists of a pair of coils .12 which are force fitted to the cores II I whose upper extremities are tapped to receive the screws l3, by virtue of which the cores are suspended from the bridge portion 2 in spaced relation. The knurled lower ends of the cores II p are enlarged and extend through apertures in the yoke 14. The diameter of the apertures in yoke l4 through which the enlarged knurled ends of the cores ll extend is slightly less than the outside diameter of the lower core ends so that by projects at each end to form integral extensions which the rear edges of the vertical legs of permanent magnet l abut. Extending upwardly from the center of the yoke [4 are two spaced arms or projections 15 (a portion of one only, is seen in Fig. 1) each of which is provided with a circular aperture which constitutes bearings for the pin l6. 7

The armture "is of sufficient length to extend from one core I l to the other and is spaced from the lower extremities thereof. The armature is provided with oppositely disposed upturned integral projections l8 which are in substantial alignment-with the projections l5 of yoke 14 and are provided with corresponding circular apertures [9 into which the ends of the pin 16 extend, the pin, therefore, constituting a support for the ar mature. The pin I6 is preferably staked in the armature apertures 19. I

To the right of the forward armature extenfully described hereinafter.

sion l3 (viewing Fig. 1), a thin sheet spring 20 is riveted or otherwise secured to the inner face of armature IT, a indicated at 2|. The spring 20, preferably of nickel-silver, extends to the left from its point of attachment to the armature I! to the outer extremity thereof and covers substantially the entire face of that portion of the armature. On its under surface, that is, the surface towards the armature, the spring 20 is provided with a pair of bosses 22 which abut against the armature and maintain the spring spaced therefrom. At its extreme outer end the spring is provided with a single boss 23 on its upper surface which engages the lower face of the core ll opposite which the spring. is located, when the armature is actuated, as will be more A non-magnetic armature stop,.2'4 integrally associated with the armature IB is located in such a position on the upper surface of the armature as to normally engage the lower extremity of th'eright-hand core II.

A striker rod 25 is staked to the forward armature extension I8 and extends vertically therefrom through an aperture in the bridge-piece 2. The upper end of the striker rod 25 is provided with a hooked portion which is recessed in a centrally located circumferential groove in the striker Ill;

A biasing coil spring 2t has one end also staked tothe forward armature projection I3 and its free end located in one of three slots 21 located on the edge of a common insulating spool head 28. The spool head 28 isa relatively stiff rectangular strip of insulating material and is provided with two spaced apertures through which the reduced upper ends of cores l I extend. Also staked to the forward armature projection I8 is a wire-like member 30 having a reversely curved free end. Thismember constitutes an adjustable stop which serves to limit the stroke of the armature and to thus adjust the stroke of the clapper rod 25 and regulate the sound output of the ringer. may be moved nearer the yoke I4 to limit the armature stroke.

Referring to Fig. 4, it will be noted that the ringer R, which represents the ringer of the present invention, is connectedto the telephone line L byway of a cold cathode gas discharge tube T. Direct current with superimposed alternating current from source S is employed to actuate the ringer R through the'medium of the tube T. The tube T acts in: the capacity of a rectifier so that the ringer R is operated by rectified current pulses. It is intended that the elements T and R represent the signalingequipment at one of a plurality of stations associated with the party line L,.the other stations (not shown) being provided with similar equipment connected to either the tip or ring conductors of the line L in such a manner as to selectively respond to polarized impulses. associated with line L is applied thereto in the well-known manner and impressed on the control electrodes of tube T, the tube breaks down permitting rectified impulses to traverse the windings of the ringer R.

The direction of therectified pulses through the .ringer coils is such as to cause the armature l1 torotate in a clockwise-direction with the pin l6 serving'as'the axis of rotation. In other words,

the direction of current through the coils I2 is such as to produce a flux which adds to the permanent magnet flux in the left air-gap, viewing -1 By bending, the free end of stop 30 When current from the signaling source of a compass needle.

Fig. 1 (air-gap a of Fig. 5) and subtracts in the right air-gap (air-gap b of Fig. 5). As the left side of the armature is moved towards its oppositely disposed magnet core, the boss 23 of spring 20 engages the core end, causing the spring to fiex about the bosses 22 which act as a fulcrum. The flexing of spring 20 introduces a force which increases in magnitude as the armature approaches the core and with the extent to which the spring is flexed. The purpose of this force will readily appear from the following description which is made with particular reference to Fig. 5. When the armature l1 reaches the limit of its clockwise rotation, the striker 10 which, by means of the rod 25 is carried by the armature, strikes the gong 6 to cause it to vibrate. At the terminationjof the rectified impulse through the ringer windings l2, the armature. is caused to return to its normal position under the action of spring 26, which is so tensioned as to restore the armature with suficient force to cause the striker H) to strike the gong l and cause. it to vibrate.

to cause the operation of gong 1 by the striker [0, since there is no reversal of current in they ringer windings to effect a reversal of the flux in the armature air-gaps and the consequent counter-clockwise rotation of the armature. It

will be noted that the springs 20 and 26 both function so as to oppose the clockwise movement of the armature I! caused by the energization of the ringer coils [2. The biasing effects of the two springs are thus additive.

The elements which constitute thepermanent.

magnetic circuit of the ringer are schematically illustrated and comprise the permanent magnet l, the bridge-piece 2, the magnet'cores H and the armature H which is shown, for simplicity, pivoted at its transverse center line. The permanent magnet I is so magnetized that the point designated N will repel the north-seeking pole rent pulse, the armature I1 is rotated in a clock-- wise direction as hereinbefore mentioned. As the armature starts to rotate; the length of air-gap or decreases and that of air gap b increases so that the reluctance of the left magnetic pathdecreases and that of the right path increases; There are, therefore, two forces, due to the permanent magnet flux acting upon the armature and though these two forces do not each vary as a linear function of the distance moved by the armature, their resultant does vary substantially in this manner and is substantially proportional to the armature displacement over the working range of the armature. There. is; ac-

cordingly a greater forceldue to the. permanentmagnetic air-gap flux) tending to rotate the armature in a clockwise direction thantendstorotate the armature in a counter-clockwise direction and this force increases in magnitude as the armature continues to rotate until it reaches-a It is. essential that the spring 26 func ion to restore the armature with sufficient force The permanent magnetic" flux, therefore, emanating from the point N will traverse the two parallel paths: indicated by the- If it is assumed that the reluc-- maximum when the armature is fully actuated. When the energizing current is removed or interrupted, the armature is still acted upon by this force and would remain in its operated position due to this force unless some mechanical means was furnished to overcome this force and restore the armature to normal. The force which tends Usually such ringers are provided with an ar-- mature biasing spring which functions to restore the armature to normal position when the ringer is deenergized. Heretofore, such a spring was necessarily pretensioned to an appreciable extent which would insure its being sufficiently tensioned, when the armature was fully operated, to at least overcome the negative stiffness due to the permanent magnetic air-gap flux and return the armature to its normal'position. Obviously, to apply an appreciable initial tension to the armature biasing spring necessitates a relatively large current to energize the ringer and overcome this initial bias, thereby reducing the sensitivity of such ringers.

The sensitivity of the ringer of the present invention is materially increased by the use of the armature balancing spring 20, which, as hereinbefore described, functions to apply a force of opposition or to impart a positive stiffness to the armature. This opposition force increases as the force due to the negative stiffness of the permanent magnetic air-gap flux increases. Since this negative stiffness is a measurable force, the spring 20 may be designed so that its stiffness will balance as closely as possible the negative stiffness. The armature is therefore acted upon by two opposing forces which, within the operating range of the armature, are at all times substantially equal and accordingly is maintained in a condition of balance in so far as the permanent magnetic air-gap flux is concerned. The biasing spring 26 can then be adjusted with comparatively low tension to always return the armature to normal since it is not called upon to overcome the negative stiffness due to the permanent magnetic air-gap flux. With the biasing spring adjusted to comparatively low tension, the value of current required to operate the ringer is correspondingly reduced, thereby rendering the ringer operable on lower current pulses than would otherwise be possible and a relative ease of adjustment is, at the same time, maintained since the biasing spring 26 acts in the capacity of a vernier to the balancing spring.

The magnitude of the positive stiffness of the balancing spring, as hereinbefore mentioned, is determined by the physical characteristics and dimensions thereof. These dimensions and characteristics are selected to impart a natural stiffness to the spring such that it balances as closely as possible the negative stiffness due to the permanent magnetic air-gap flux.

With the ringer of this invention it will be noted that, when the armature is fully actuated, it is acted upon by the permanent magnetic airgap flux which tends to hold it operated and by the force exerted by spring 20 which tends to restore the armature to normal. Since, by design, these two forces are equal, the armature is in a condition of substantial balance when the ringer becomes deenergized and the spring 26 to facilitate themovement of the armature during-its operation and which acts to prevent the a need only betension'ed' so as to just'overcome this balance to restore the armature.

What isclaimed is: 1. In an electromagnetically operated device, a core, an armature spaced from said core, means for energizing said device to cause said armature to be actuated and to approach said core, a permanent magnet so disposedwith respect to said armature and said core as to produce a flux which tends to hold said armature and'core to-- gether with a force of measurable magnitude When said device is deenergized, a biasing spring for restoring said armature to normal when said device is deenergized, and means independent of said biasing spring for applying to said armature a force equal to and opposite in effect to said force of measurable magnitude.

*2. In an 'electromagneticallyoperated device, a core, an armature spaced from said core, means for energizing said device to cause said armature to be actuated and to contact said core, a permanent magnet so disposed with respect to said armature and said core as to produce afiux which tends to hold said armature actuated with a force of measurable magnitude when said device is deenergized, a biasing spring for restoring said armature to normal, and means independent of said biasing spring for applying to said armature, when fully actuated, a force equal to and opposite in effect to said force of measurable magnitude, said means comprising a flexible spring carried by said armature and interposed between said armature and said core.

3. In an electromagnetically operated device, a core, an armature spaced from said core, means for energizing said device to cause said armature to approach said core, a permanent magnet so disposed with respect to said armature and core as to produce a flux which tends to aid in the movement of said armature. with a measurable force which increases in magnitude as the armature approaches the core, means comprising a flexible spring carried by said armature and interposed between said armature and said core all positions of the armature balances said measurable force, and a biasing spring independent of said balancing means for said armture.

4. In an electromagnetioally operated device, an electromagnet having a pole, a centrally pivoted armature spaced from said pole by an air-gap, means for energizing said electromagnet to cause said armature to approach said electromagnet pole, a permanent magnet for producing a flux in said air-gap which imparts to said armature a negative stiffness which tends to facilitate the movement of said armature when said electromagnet is energized and to prevent the return of said armature when said electromagnet is deenergized, and means located in said air-gap for imparting a positive stiffness to said armature upon the energization of said electromagnet which balances the negative stiffness due to the permanent magnet air-gap flux.

5. In an electromagnetically operated device, an electromagnet having a pole, a centrally pivoted armature spaced from said pole byan airgap, means for energizing said electromagnet to cause said armature to approach said electromagnet pole and decrease the length of said airgap, a permanent magnet for producing a flux in said air-gap which-imparts to said armature a negative stiffness which increases in magnitude as the armature approaches the electromagnet pole and which tends to facilitate the movement of the armature when the electromagnet is. energized and. to prevent the return of the armature when the electromagnet is deenergized, and means located in the air-gap for impartingto said armature a positive stiffness which increases in magnitude as the armature negative stifiness increases and is at all positions of the'armature equal thereto. I

6. In a telephone ringer, a pair of electromagnet poles, an armature spaced from said poles and having an axis of rotation which is in substantial alignment with the transverse center line of'the armature, a permanent magnet so disposed with respect to said armature and said e1ectro magnet poles as to cause each endof said armature to experience a force which tends to. move the armature ends towards their respective electromagnet poles, means for energizing the elec- 15 one of said poles.

tmmagnet to cause one. end of said armature to approach its corresponding electromagnet pole and the other end to move away from its corresponding electromagnet pole whereby the forceexerted by said permanent magnet on one end of said armature increases and the force exerted on the other end of said armature decreases, and means for counterbalancing the increasing force efiected by said permanent magnet when said armature is operated, said means comprising asheet spring anchored to said armature at one side of its transverse center line and extending beyond the other side thereof to the end of said armature and interposed between the armatureand JAMES D. HUBBELL. CHARLES F. WIEBUSCH. 

